Split-Tendon Medial Transposition of Lateral Rectus for Pediatric Complete Oculomotor Palsy.

BACKGROUND: Split-tendon medial transposition of lateral rectus (STMTLR) for complete oculomotor palsy can correct large angles of exotropia in adults, but outcomes are variable, and complications are frequent. Only a few pediatric cases have been reported, and further insight is needed to assess the child's alignment outcomes and ability for postsurgical gain of function. The aim of our study is to report the outcomes of this surgical procedure in pediatric cases of complete oculomotor palsy. METHODS: A retrospective review of outcomes was conducted on 5 consecutive patients with complete oculomotor palsy treated with STMTLR by a single surgeon (V.S.S.) between 2015 and 2021 at tertiary referral centers. Primary outcome was postoperative horizontal alignment, and secondary outcome was demonstration of gain-of-function activity in the field of action of the paretic medial rectus muscle. RESULTS: Five cases of pediatric complete oculomotor palsy underwent surgical treatment with STMTLR. Subjects averaged 5.3 years old (range 10 months-16 years). Two were female. Etiologies were heterogeneous, and all presented with unilateral (n = 2) or bilateral complete oculomotor palsy with exodeviations ranging from 45 to >120 prism diopters. Two subjects had bilateral disease secondary to military tuberculosis with CNS involvement. A third subject presented iatrogenically with complete bilateral third nerve palsies secondary to removal of a nongerminomatous germ cell tumor (NGGCT) of the pineal gland. The 2 remaining subjects had monocular involvement in their right eye, 1 from compressive neuropathy after a cavernoma midbrain hemorrhage, and 1 from a congenital right oculomotor palsy. All patients were observed to have stable ocular alignment for a period of at least 6 months before surgery. Unilateral STMTLR was performed in all cases except the subject with NGGCT, in which bilateral STMTLR was performed. Measurement of alignment permanence out to 1-3 years postop resulted in an average correction of 40.83 prism diopters (range 37.5-45 prism diopters) per operated eye. Four of 5 subjects regained limited but active adduction eye movements, and the 2 unilateral cases demonstrated improved convergence. None of the subjects experienced significant complications. CONCLUSIONS: STMTLR was a safe and effective approach for the surgical correction of complete pediatric oculomotor palsy in our case series. In addition, pediatric patients may benefit from STMTLR with immediate gain-of-function activity in the transposed lateral rectus muscle, which supports the hypothesis that children have a dynamic and adaptive neuroplasticity of visual target selection that predominates established agonist/antagonist neural signaling.

An unusual presentation of bilateral optic pathway glioma in Crouzon Syndrome.

Crouzon Syndrome is a genetic craniosynostosis disorder associated with a high risk of ophthalmologic sequelae secondary to structural causes. However, ophthalmologic disorders due to intrinsic nerve aberrations in Crouzon Syndrome have not been described. Optic pathway gliomas (OPGs) are low grade gliomas that are intrinsic to the visual pathway, frequently associated with Neurofibromatosis type 1 (NF-1). OPGs involving both optic nerves without affecting the optic chiasm are rarely seen outside of NF-1. We report an unusual case of bilateral optic nerve glioma without chiasmatic involvement in a 17-month-old male patient with Crouzon Syndrome without any clinical or genetic findings of NF-1. This case suggests that close ophthalmologic follow up and orbital MRIs may benefit patients with Crouzon Syndrome.

Early radiotherapy preserves vision in sporadic optic pathway glioma.

BACKGROUND: Sporadic optic pathway/hypothalamic gliomas represent a unique entity within pediatric low-grade glioma. Despite favorable survival, location makes treatment difficult and local progression debilitating. This study is a longitudinal assessment of visual acuity (VA) among children treated within the last 2 decades. METHODS: Clinical characteristics were abstracted for patients treated from 2000 to 2018 at Texas Children's Cancer Center in Houston. Ophthalmologic data taken at 3- to 6-month intervals were examined with age-appropriate VA metrics converted to the LogMAR (logarithm of the minimum angle of resolution) scale. Kaplan-Meier blindness-free survival (BFS) curves, calculated as time-to-bilateral functional blindness (LogMAR ≥0.8 in both eyes), were calculated for patients receiving early radiation therapy (RT; upfront or as first-line salvage treatment) or chemotherapy (CT) and evaluated using the log-rank test. RESULTS: Thirty-eight patients with a median follow-up of 8.5 years (range, 2-17 years) were identified. Median age at diagnosis was 3 years (interquartile range, <1-6 years). Early RT was administered in 11 patients (29%). Twenty-seven patients (71%) were treated primarily with CT, initiated at a median age of 3.5 years (range, <1-11 years). Eight patients in the CT group did eventually require RT secondary to VA loss and following multiple lines of CT. Median age at RT for all patients was 11 years (range, 3-17 years). BFS rates were 81% at 5 years and 60% at 8 years for CT and 100% at 5 and 8 years for early RT (P = .017). CONCLUSIONS: In a contemporary cohort, early RT, defined as initial or first-line salvage therapy, was found to have superior BFS for appropriately selected patients with sporadic optic pathway/hypothalamic gliomas. LAY SUMMARY: Children with low-grade brain tumors of the optic pathway generally have excellent long-term survival; however, given the location of these tumors, there can commonly be threatened vision if the tumor grows. Although radiation is generally deferred in children on the basis of legitimate concerns regarding the effects on the developing brain, it may represent a vision-preserving therapy for well-selected older patients.

Prevalence of Adrenal Insufficiency and Glucocorticoid Use in Pediatric Pseudotumor Cerebri Syndrome.

BACKGROUND: The pathophysiology underlying pseudotumor cerebri syndrome (PTCS) is complex and not well understood. There are clear differences between PTCS in adults and pediatrics. Few and isolated case reports have suggested that adrenal function may be involved, yet no large cohort study has examined this relationship. METHODS: We conducted a retrospective single-center study of children who presented with a diagnosis of PTCS and had cortisol testing measured between January 2010 and September 2019. We included all subjects meeting the revised PTCS diagnostic criteria after the chart review. Based on morning, random or 1-µg cosyntropin stimulated cortisol levels, adrenal functioning was classified as: (1) insufficient (peak cortisol <16 µg/dL and AM cortisol <5 µg/dL), (2) at risk (peak cortisol 16-20 µg/dL, AM cortisol 5-13 µg/dL, or random <13 µg/dL), or (3) sufficient (peak cortisol >20 µg/dL and AM or random cortisol >13 µg/dL). RESULTS: A total of 398 individuals were reviewed, and 64 were included for analysis. Of these, 40.6% were men, of mixed race and ethnicity with a mean age of 10.5 (SD 4.7) years. Of these, 23% and 52% had insufficient or at-risk cortisol levels. The majority of those in the insufficient (70%) or at-risk (80%) groups were exposed to topical, nasal, or inhaled glucocorticoids but not systemic. Only 60% and 12% of those with PTCS with insufficient or at-risk cortisol testing, respectively, underwent definitive testing with a stimulation test. CONCLUSIONS: Glucocorticoid use and hypocortisolism are prevalent in PTCS and need consideration as a potential underlying cause. Most children had insufficient or at-risk cortisol levels, and many did not undergo further testing/workup. Children who present with PTCS, particularly young, males should be evaluated for adrenal insufficiency and its risk factors, including nonsystemic steroids. Prospective studies are necessary to further evaluate the effect of cortisol in relation to pediatric PTCS.

Double Vision and Gait Ataxia in an Immunocompetent 9-Year-Old Girl With Intracranial Phaeohyphomycosis.

ABSTRACT: A 9-year-old girl presented with morning headaches associated with vomiting, gait ataxia, and facial and ocular motor nerve palsies. Her initial imaging was concerning for demyelinating disease. After extensive infectious and rheumatologic workup returned negative, she was treated twice with intravenous immunoglobulin and intravenous steroids with near-complete resolution each time. She returned, however, with worsening neurologic deficits and imaging revealing focal ischemic infarction in the brainstem as well as new-onset hydrocephalus. A multispecialty workup was initiated without conclusive diagnosis. A novel, noninvasive test for plasma cell-free DNA established a diagnosis of Cladophialophora bantiana that was confirmed and validated by a brain biopsy taken during a clinical decompensation. Treatment was initiated with systemic voriconazole and intraventricular amphotericin B.

Phenotypic expansion of Bosch-Boonstra-Schaaf optic atrophy syndrome and further evidence for genotype-phenotype correlations.

Bosch-Boonstra-Schaaf Optic Atrophy Syndrome (BBSOAS) is an autosomal dominant neurodevelopmental disorder caused by loss-of-function variants in NR2F1 and characterized by visual impairment, developmental delay, and intellectual disability. Here we report 18 new cases, provide additional clinical information for 9 previously reported individuals, and review an additional 27 published cases to present a total of 54 patients. Among these are 22 individuals with point mutations or in-frame deletions in the DNA-binding domain (DBD), and 32 individuals with other types of variants including whole-gene deletions, nonsense and frameshift variants, and point mutations outside the DBD. We corroborate previously described clinical characteristics including developmental delay, intellectual disability, autism spectrum disorder diagnoses/features thereof, cognitive/behavioral anomalies, hypotonia, feeding difficulties, abnormal brain MRI findings, and seizures. We also confirm a vision phenotype that includes optic nerve hypoplasia, optic atrophy, and cortical visual impairment. Additionally, we expand the vision phenotype to include alacrima and manifest latent nystagmus (fusional maldevelopment), and we broaden the behavioral phenotypic spectrum to include a love of music, an unusually good long-term memory, sleep difficulties, a high pain tolerance, and touch sensitivity. Furthermore, we provide additional evidence for genotype-phenotype correlations, specifically supporting a more severe phenotype associated with DBD variants.

Syndromic Multisuture Craniosynostosis With Associated Anterior Segment Dysgenesis, Optic Nerve Hypoplasia, and Congenital Glaucoma.

Patients with craniosynostosis with subnormal vision due to papilledema and/or exposure-related corneal decompensation are well documented in the literature; however, there is only a single prior documented case of vision compromise secondary to anterior segment dysgenesis and glaucoma in this patient population. This report highlights a case of syndromic craniosynostosis with advanced corneal decompensation and anterior segment dysgenesis that was masked and ultimately delayed the diagnosis of congenital glaucoma.

Five-Year-Old Boy With Behavioral Changes and Papilledema.

A 5-year-old boy had initial symptoms of behavioral changes, nausea, vomiting, headache, weight loss, and progressive vision failure. Brain MRI revealed abnormal signal intensity in both optic nerves, the optic chiasm, the right medial temporal lobe, and tissues surrounding the right supraclinoid internal carotid artery with associated leptomeningeal and spinal cord enhancement. After nondiagnostic dural and spinal arachnoid biopsies, a temporal lobe biopsy was diagnostic for a rare malignant peripheral nerve sheath tumor.

Systemic Amyloidosis and Extraocular Muscle Deposition.

Isolated amyloid deposition in an extraocular muscle is a rare event but can be a presenting feature of systemic amyloidosis. A 67-year-old woman with an acquired exotropia and hypertropia was found to have unilateral diffuse extraocular muscle enlargement on magnetic resonance imaging. Owing to the progressive nature of her strabismus and the negative laboratory testing for thyroid disease, she underwent an extraocular muscle biopsy that revealed amyloid deposition. Further workup demonstrated a monoclonal gammopathy consistent with systemic amyloidosis. This case demonstrates the need to consider amyloidosis in the differential diagnosis of patients presenting with an atypical acquired strabismus. We review other reports of isolated amyloid deposition in extraocular muscles and its association with systemic amyloidosis, emphasizing the importance of the ophthalmologist in the early recognition of this disease to prevent irreversible, life-threatening end organ damage.

Pediatric autoimmune retinopathy and optic neuropathy: a case report and a review of the literature.

Purpose: The purpose of the study was to present a rare case of pediatric bilateral optic neuropathy and retinopathy, which was consistent with a diagnosis of autoimmune retinopathy. We also reviewed the most current literature and phenotypes associated with reported pediatric cases of autoimmune retinopathy. Design: The design of the study was a case report, with a retrospective case series literature review. Subjects: This study incorporated data from six subjects, with one presenting as an original case report and five being identified from the English-language literature published to date. Materials and methods: The materials and methods involved a descriptive analysis of fundus findings, electrophysiologic testing, serum autoantibody testing, optical coherence tomography (OCT), brain MRI scanning, and fluorescein angiography, which were performed where available. Main outcome measures: The study evaluated the clinical presentation and treatment outcomes of all subjects and followed their visual function over time. Results: All six subjects had retinal abnormalities that were documented on imaging, while five out of the six subjects had optic nerve abnormalities. Electrophysiologic testing was performed on three subjects, all of whom recorded abnormal results. An underlying neoplastic disorder was described for four subjects. Serum autoantibody testing results were available for four subjects. The serum testing included using antibodies against a 22-kDa antigen, a 35-kDa optic nerve-derived antigen, a 62-kDa antigen, enolase, recoverin, tubulin, and pyruvate kinase M2. Our subject presented 12 years after resection of a ganglioglioma with asymmetric bilateral vision loss, disc edema in one eye, advanced disc pallor in the fellow eye, and bilateral subtle retinal infiltrates, despite having a normal fluorescein angiogram. OCT demonstrated asymmetric ganglion cell layer thinning, which is consistent with the vision loss. Our subject also had abnormal brain MRI findings of widespread pachymeningeal enhancement, but he had a normal cerebrospinal fluid composition. He was initially treated with high-dose pulse steroids, followed by intravenous immunoglobulin therapy. He experienced partial visual recovery in both eyes. Conclusions: Pediatric autoimmune retinopathy and optic neuropathy are rare diseases that can present with unique signs and symptoms. In pediatric patients who present with symptoms of subacute progressive vision loss with negative inflammatory workups, a history of prior neoplasm, and/or clinical findings of progressive retinopathy or optic neuropathy, an autoimmune process should be considered in the differential.

Panuveitis and optic neuropathy following SARS-COV-2 in the absence of multisystem inflammatory syndrome in a child.

Purpose: To describe the presentation of a healthy 8-year-old female referred to a pediatric ophthalmology clinic with blurred vision and concern for bilateral uveitis. Observations: The patient was diagnosed with COVID-19 two weeks prior to the onset of ocular symptoms. An examination revealed bilateral pan-uveitis and patient underwent an extensive work-up for an underlying cause that was unremarkable. Two years following the initial presentation, she has not had any evidence of recurrence. Conclusions and Importance: This case highlights the potential for COVID-19 to be temporally associated with ocular inflammation and underscores the importance of recognizing and investigating such manifestations in pediatric patients. The mechanism by which COVID-19 may lead to an immune response that affects the eyes is not fully understood, but it is believed to be related to an overactive immune response triggered by the virus. Further studies are needed to better understand the potential relationship between COVID-19 and ocular manifestations in pediatric patients.

Pediatric Bartonella henselae neuroretinitis masking co-infections.

PURPOSE: Neuroretinitis (NR) is an inflammatory disorder that presents with painless vision loss due to optic disc edema, peripapillary detachment, and macular lipid exudation. We report the first two documented cases of co-infections of pediatric NR due to Bartonella henselae with HSV and Toxocara cati, respectively. OBSERVATIONS: A 10-year-old female with acute right-sided facial droop, right eye pain, and acute visual loss of the right eye is diagnosed with co-infection of Bartonella and HSV retinitis and is successfully treated with acyclovir, rifampin, and doxycycline. A 13-year-old female with progressive visual loss of the left eye is diagnosed with co-infection of Bartonella and ocular toxocariasis and is successfully treated with doxycycline, rifampin, prednisolone, and albendazole. CONCLUSIONS AND IMPORTANCE: Early recognition and multi-modal treatment is necessary to prevent delayed diagnosis and treat the underlying NR causes for optimal visual recovery.

Longitudinal neurological analysis of moderate and severe pediatric cerebral visual impairment.

Introduction: Cerebral visual impairment (CVI) results from damage to cerebral visual processing structures. It is the most common cause of pediatric visual impairment in developed countries and rising in prevalence in developing nations. There is currently limited understanding on how neurologic, developmental, and ophthalmic factors predict outcome for pediatric CVI. Method: A retrospective manual chart review of pediatric CVI patients seen at the tertiary pediatric hospital neurology and neuro-ophthalmology service between 2010 and 2019 was conducted. Patients were stratified into severity groups (based on a custom CVI grading score), and followed over time to identify outcome predictors. Collected baseline characteristics included perinatal, genetic, developmental, and neurologic history, along with neuroimaging and fundoscopic findings on examination. Longitudinal data collected included age, seizure control, and type of therapy received. Linear mixed-effect models were used for longitudinal CVI grade outcome analysis. Results: A total of 249 individuals spanning 779 patient visits were identified. Mean age at diagnosis was 18.8 ± 16.8 months (2-108 months). About 64.3% were born at term age. Perinatal history revealed hypoxic ischemic encephalopathy (HIE) in 16.5%, intraventricular hemorrhage (IVH) in 11.6%, and seizures in 21.7%. At presentation, 60.3% had a diagnosis of cerebral palsy and 84.7% had developmental delay. Among all subjects, 78.6% had epilepsy; 33.8% had an epileptic encephalopathy, with spasms/hypsarrhythmia being most common. Abnormal neuroimaging was present in 93.8%. Genetic anomalies were present in 26.9%. Baseline visual examination revealed no blink-to-light (BTL) in 24.5%; only BTL in 34.5%, fixation/tracking in 26.5%, and optokinetic drum follow in 14.4%. Longitudinal data analysis showed that perinatal history of HIE, a positive epilepsy history, using multiple (≥3) epilepsy medications, cerebral palsy, and abnormal fundoscopic findings were all negatively associated with CVI grade change over time. After controlling for significant confounders, receiving any type of therapy [early childhood intervention (ECI), physical and occupational therapy (PT/OT), refractive error correction or glasses] was significantly associated with longitudinal improvement in CVI grade compared to patients who did not receive any therapy, with glasses yielding the largest benefit. Conclusion: This study offers extensive insights into neurologic, developmental and ophthalmologic features in patients with moderate to severe CVI. In concordance with previous findings, aspects of perinatal history and epilepsy/seizure control may help inform severity and prognosis in the general neurology or ophthalmology clinic. Conversely, these aspects, as well as genetic and specific epilepsy traits may alert vision health care providers in the clinic to pursue visual evaluation in at-risk individuals. Longitudinal follow-up of CVI patients showed that interventional therapies demonstrated vision function improvement greater than no therapy and maturational development.

Visual preservation in congenital orbital fibrosis.

OBJECTIVE: Congenital orbital fibrosis (COF) is a nonprogressive, unilateral, congenital process in which variable fibrosis is demonstrated in the orbit, resulting in restrictive strabismus, upper eyelid malposition, and axial displacement of the globe. We present 4 new pediatric cases of COF and discuss factors that impact visual development. We also describe a patient with local compressive optic neuropathy/edema who underwent optic nerve sheath fenestration (ONSF) for visual preservation. DESIGN: Literature review and retrospective case series. RESULTS: Four male COF patients (mean age of 11 months) were examined. Two patients presented with decreased ocular motility of the affected eye. Two patients presented with exophthalmos, and one presented with enophthalmos. Two patients presented with ptosis, and one presented with eyelid retraction. Two patients presented with optic nerve atrophy, and one presented with optic nerve edema. Magnetic resonance imaging demonstrated involvement of the superior, medial, and inferior rectus and superior oblique muscles in 3 patients and the lateral rectus and inferior oblique muscles in 2 patients. Three patients underwent orbitotomy. Histology was consistent with fibrosis. Three patients demonstrated amblyopia, and 2 responded to treatment. The patient with optic nerve edema underwent ONSF. At 4 months' follow-up, the edema had resolved. CONCLUSIONS: COF can present with either anterior or posterior globe displacement. Patients must undergo a complete ophthalmic evaluation to identify modifiable factors. Strabismus and ptosis should be addressed for optimal visual development. Amblyopia therapy should be instituted quickly. Patients who present with active optic nerve edema may benefit from ONSF for local compressive optic neuropathy.

Neuro-Ophthalmological Manifestations of Craniosynostosis: Current Perspectives.

Craniosynostosis, a premature fusion of cranial sutures that can be isolated or syndromic, is a congenital defect with a broad, multisystem clinical spectrum. The visual pathway is prone to derangements in patients with craniosynostosis, particularly in syndromic cases, and there is a risk for permanent vision loss when ocular disease complications are not identified and properly treated early in life. Extensive advancements have been made in our understanding of the etiologies underlying vision loss in craniosynostosis over the last 20 years. Children with craniosynostosis are susceptible to interruptions in visual input arising from strabismus, refractive errors, and corneal damage; any of these aberrations can result in understimulation of the visual cortex during childhood neurodevelopment and permanent amblyopia. Elevated intracranial pressure resulting from abnormal cranial shape or volume can lead to papilledema and, ultimately, optic atrophy and vision loss. A pediatric ophthalmologist is a crucial component of the multidisciplinary care team that should be involved in the care of craniosynostosis patients and consistent ophthalmologic follow-up can help minimize the risk to vision posed by such entities as papilledema and amblyopia. This article aims to review the current understanding of neuro-ophthalmological manifestations in craniosynostosis and explore diagnostic and management considerations for the ophthalmologist taking care of these patients.

OUTER RETINAL INJURY SECONDARY TO MEMBRANE PEELING WITH INTERNAL LIMITING MEMBRANE FORCEPS.

PURPOSE: To present a case of visually significant retinal injury due to internal limiting membrane (ILM) peeling using ILM forceps alone. METHODS: Case report. RESULTS: A 60-year-old woman who underwent ILM peeling for an epiretinal membrane presented with linear central scotomata. Peeling had been initiated and performed with ILM forceps alone, without the use of other surgical instruments. Fundus examination and spectral domain optical coherence tomography imaging confirmed the presence of several discrete areas of inner and outer retinal injury in the macula, which corresponded to her scotomata. CONCLUSION: This is a case of visually significant retinal injury due to ILM peeling that was performed with ILM forceps alone. Improper peeling technique can transmit injurious forces to the retina. Surgeons must be mindful of the biomechanical forces involved in ILM peeling to minimize traction on the retina.

Pediatric Autoimmune Ocular Myasthenia Gravis: Evaluation of Presentation and Treatment Outcomes in a Large Cohort.

BACKGROUND: In autoimmune myasthenia gravis (MG), autoantibodies target the neuromuscular junction. Ocular myasthenia gravis (OMG) is localized, affecting only extraocular and/or levator palpebrae muscles. OMG presents across all ages, varying in presentation, treatment modalities, and outcomes. Recently, there have been advances in MG/OMG treatment; their utilization and effectiveness are an important part of optimal disease management. METHODS: We completed a retrospective chart review of children aged 18 years or younger with a confirmed diagnosis of OMG presenting from 2002 to 2019. RESULTS: Forty-two patients were included with mean age at presentation of 8.5 years (2 to 18 years). Twenty-one patients (50%) had positive antibodies; 90% had acetylcholine receptor antibodies. Ten patients developed generalized symptoms with mean time to generalization of 13.6 months. Multiple logistic regression showed that older age of onset was a trend predictive factor (P = 0.054; odds ratio 1.17) for generalized disease. All patients were treated with pyridostigmine. Immunomodulating agents included steroids (15), mycophenolate mofetil (four), and intravenous immunoglobulin (one). Three patients underwent thymectomy. Twenty patients reached minimal manifestation status, and 12 achieved remission. Gender, race, and positive antibody status were not statistically significant predictors for advanced immunosuppressive therapy. CONCLUSIONS: We summarize one of the largest cohorts of pediatric patients with OMG who have undergone up-to-date diagnostic and therapeutic regimens. The predictors of outcome and treatment pathway for OMG patients suggested by this report may be further elucidated by future prospective studies.

Restricted patterns of Hoxd10 and Hoxd11 set segmental differences in motoneuron subtype complement in the lumbosacral spinal cord.

During normal vertebrate development, Hoxd10 and Hoxd11 are expressed by differentiating motoneurons in restricted patterns along the rostrocaudal axis of the lumbosacral (LS) spinal cord. To assess the roles of these genes in the attainment of motoneuron subtypes characteristic of LS subdomains, we examined subtype complement after overexpression of Hoxd10 or Hoxd11 in the embryonic chick LS cord and in a Hoxd10 loss-of-function mouse embryo. Data presented here provide evidence that Hoxd10 defines the position of the lateral motor column (LMC) as a whole and, in rostral LS segments, specifically promotes the development of motoneurons of the lateral subdivision of the lateral motor column (LMCl). In contrast, Hoxd11 appears to impart a caudal and medial LMC (LMCm) identity to some motoneurons and molecular profiles suggestive of a suppression of LMC development in others. We also provide evidence that Hoxd11 suppresses the expression of Hoxd10 and the retinoic acid synthetic enzyme, retinaldehyde dehydrogenase 2 (RALDH2). In a normal chick embryo, Hoxd10 and RALDH2 are expressed throughout the LS region at early stages of motoneuron differentiation but their levels decline in Hoxd11-expressing caudal LS segments that ultimately contain few LMCl motoneurons. We hypothesize that one of the roles played by Hoxd11 is to modulate Hoxd10 and local retinoic acid levels and thus, perhaps define the caudal boundaries of the LMC and its subtype complement.